iron(III) chloride in dichloromethane byproducts: BCl2(OC2H5); slow addn. of boronate to BCl3 soln. contg. FeCl3 under N2, 0°C, within 10 min; stirring at 0°C, 1 h and at 25°C, 1 h; evapn.; extn. (CH2Cl2); evapn.; distn.;